/* vim: set fileencoding=utf-8:
 *
 *                   GNU GENERAL PUBLIC LICENSE
 *                       Version 2, June 1991
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; see the file COPYING.  If not, write to
 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 * 
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <ctype.h>

uint8_t chksum8(uint8_t* buf, int nr_bytes)
{
    uint8_t chksum = 0;
    int i;

    for (i = 0;i < nr_bytes;i++) {
        chksum += buf[i];
    }

    return chksum;
}

//modbus 16bits crc
//
//  polygon     : 0x1_8005  (reverse 0x0_A001)
//  bitreverse  : True
//  crcinit     : 0xFFFF
//  xormask     : 0x0000    (no output xor need)
//
static const uint16_t _crc_table[256] = {
    0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0,
    0x0280, 0xc241, 0xc601, 0x06c0, 0x0780, 0xc741,
    0x0500, 0xc5c1, 0xc481, 0x0440, 0xcc01, 0x0cc0,
    0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
    0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0,
    0x0880, 0xc841, 0xd801, 0x18c0, 0x1980, 0xd941,
    0x1b00, 0xdbc1, 0xda81, 0x1a40, 0x1e00, 0xdec1,
    0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
    0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0,
    0x1680, 0xd641, 0xd201, 0x12c0, 0x1380, 0xd341,
    0x1100, 0xd1c1, 0xd081, 0x1040, 0xf001, 0x30c0,
    0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
    0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0,
    0x3480, 0xf441, 0x3c00, 0xfcc1, 0xfd81, 0x3d40,
    0xff01, 0x3fc0, 0x3e80, 0xfe41, 0xfa01, 0x3ac0,
    0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
    0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0,
    0x2a80, 0xea41, 0xee01, 0x2ec0, 0x2f80, 0xef41,
    0x2d00, 0xedc1, 0xec81, 0x2c40, 0xe401, 0x24c0,
    0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
    0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0,
    0x2080, 0xe041, 0xa001, 0x60c0, 0x6180, 0xa141,
    0x6300, 0xa3c1, 0xa281, 0x6240, 0x6600, 0xa6c1,
    0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
    0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0,
    0x6e80, 0xae41, 0xaa01, 0x6ac0, 0x6b80, 0xab41,
    0x6900, 0xa9c1, 0xa881, 0x6840, 0x7800, 0xb8c1,
    0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
    0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1,
    0xbc81, 0x7c40, 0xb401, 0x74c0, 0x7580, 0xb541,
    0x7700, 0xb7c1, 0xb681, 0x7640, 0x7200, 0xb2c1,
    0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
    0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0,
    0x5280, 0x9241, 0x9601, 0x56c0, 0x5780, 0x9741,
    0x5500, 0x95c1, 0x9481, 0x5440, 0x9c01, 0x5cc0,
    0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
    0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0,
    0x5880, 0x9841, 0x8801, 0x48c0, 0x4980, 0x8941,
    0x4b00, 0x8bc1, 0x8a81, 0x4a40, 0x4e00, 0x8ec1,
    0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
    0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0,
    0x4680, 0x8641, 0x8201, 0x42c0, 0x4380, 0x8341,
    0x4100, 0x81c1, 0x8081, 0x4040
};

uint16_t crc16(const void* buf, int len)
{
    uint16_t r = 0xFFFF;
    const uint8_t* ptr = (const uint8_t*)buf;

    while (len-- > 0) {
        r = (_crc_table[(r & 0xFF) ^ (*ptr++)]) ^ ((r >> 8) & 0xFF);
    }

    return r;
}

uint16_t crc16_init(void)
{
    return 0xFFFF;
}

uint16_t crc16_update(uint16_t crcvalue, const void* buf, int len)
{
    uint16_t r = crcvalue;
    const uint8_t* ptr = (const uint8_t*)buf;

    while (len-- > 0) {
        r = (_crc_table[(r & 0xFF) ^ (*ptr++)]) ^ ((r >> 8) & 0xFF);
    }

    return r;
}



